Simple Interest — A sum becomes three times in 20 years at simple interest. In how many years will it become double at the same rate?
Aptitude
Simple Interest
Difficulty: Easy
Choose an option
Answer
Correct Answer: 10 yr
Explanation
Introduction / Context:First use the tripling information to deduce the rate under simple interest, then reuse that rate to find the doubling time.
Given Data / Assumptions:
- A = 3P in 20 years (simple interest).
- Same rate is used to find time to double.
Concept / Approach:If A = 3P, then SI = 2P over 20 years. Hence P * r * 20 = 2P ⇒ r = 2/20 = 0.10 = 10% p.a.
Step-by-Step Solution:Rate r = 10% per annum.To double: need SI = P.P = P * r * t ⇒ P = P * 0.10 * t ⇒ t = 10 years.
Verification / Alternative check:At 10% for 10 years: SI = P; amount = 2P.
Why Other Options Are Wrong:8, 12, 14, 16 years do not match r = 10% derived from the tripling data.
Common Pitfalls:Carrying compound interest ideas into a simple interest setting.
Final Answer:10 yr